The present invention relates to a projectile propelling system and particularly to the RAM accelerator type of projectile propelling system.
The RAM accelerator is a recent type of projectile propelling system for accelerating heavy projectiles to hyper velocities in the range of 10 Km/s. It is based on a continuous combustion or detonation of a gaseous propulsive mixture in a gun. The gun barrel is prefilled with the mixture, and the projectile is propelled into the gun barrel and the gaseous propulsive mixture after the projectile has been accelerated by a conventional launcher, such as a light gas gun or a powder gun. The projectile is shaped in a special manner so that the flow around it creates the necessary conditions for the mixture to be detonated. The thrust is produced by the action of the high pressure of the expanding combustion or detonation products on the rear part of the projectile.
More particularly, in the RAM accelerator propelling system the driver propels the projectile in the gun barrel to an initial velocity above the detonation velocity of the gaseous propulsion mixture within the gun barrel to produce a shock wave at a front cone wall of the projectile, followed by a detonation wave applied to the rear cone wall of the projectile. The detonation wave results from the reflection of the shock wave at the barrel wall and, when applied to the rear cone wall, increases the velocity of the projectile.
This type of projectile propelling system is described in the literature, for example in Hertzberg, A, Bruckner, A. P. and Bogdanoff, D. W.: "The RAM Accelerator: A New Chemical Method of Achieving Ultrahigh Velocities", Proceedings of the 37th Meeting of the Aeroballistic Range Association, Quebec, September 1986. In the analysis given by the authors, the acceleration process comprises three main stages: (1) a preliminary acceleration stage by a conventional gun (0-0.7 Km/s); (2) an intermediate acceleration stage via a subsonic combustion process (0.7-2 Km/s); and (3) a final acceleration stage, involving detonation of the propulsive mixture.
The position of the reflected detonation wave is of critical importance to the efficiency of the RAM accelerator type projectile propelling system. Thus, if the detonation wave impinges the projectile forwardly of the rear cone wall, the high pressure of the detonation products will contribute to a drag force and will thus reduce the net thrust. On the other hand, if the detonation wave impinges the projectile too much rearwardly of the rear cone wall, then only a fraction of the rear cone area will be exposed to the high pressure gases, thereby reducing the thrust produced by the detonation wave. A difficulty in the RAM accelerator propelling system is the problem of effecting ignition of the mixture at the reflection point of the nose shock wave to obtain thrust, because this occurs only in a narrow range of projectile velocities in the conventional RAM accelerator system.